Question just for electrical linemen!

[hallerb]

First thanks for all you do, frequently in the worst weather and conditions. I am certain everyone appreciates getting their service restored. Sadly around pittsburgh Duquesne light tends to wait till a overloaded tranmsformer fries before replacing it. Even one thats tripped it thermal protection repeatedly:(

Anyhow my question. Before working on what you BELIEVE is a dead line do you short it just to be on the safe side?

I was told this by a local lineman and just want to confirm. thanks bob haller...

if you do short lines do you occasionally find one thats still live???????

[Mark and Kim Smith]

If I remember correctly, for 33kv and below, our guys hot stick and are rubber glove trained. Above, they get an outage.

[Bob]

Depending on voltage and proximity either a meter, or tick tracer is used to verify lines and equipment is non-energized prior to safety grounds being applied. Safety grounds are not really effective on the secondary side of a low voltage transformer. At 13,200 volts, there's only a few thousand amps available. Not nearly enough current to do anything spectacular with the safety ground (usually 4/0, fine strand) for the short duration that the current will be available, assuming good contact with the conductors. On the secondary side of your typical pad mount 200 kva transformer, normal current phase to ground on the secondary is on the order of 1600 amps continuous. Available shourt circuit current might be 20,000 amps or more for a while. Long enough to burn up a safety ground.

Short answer... grounds are not applied until lines are verified dead.

Grounds are occasionally accidentally applied to hot lines. It shouldn't happen if proper procedures are followed.

[hallerb]

theres was a event here a few years ago.

someone made a bad switch throw, a worker walking by a safety ground got tossed off the tower when the safety ground exploded.

worker got lifeflighted to hospital trauma unit

[maradcliff]

I'm not a lineman, so I should not answer. But, if I were dealing with the high voltage before a pole transformer, I sure as heck would not short it to test. Thats what test instruments are for. One other thing. There is always a removable fuse before a transformer, and I have always seen linemen remove it before working on a transformer. Now if they are working on the HV wires themselves, there is more of a risk.

Mark

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[Stormin Mormon]

Not a lineman.

However, I've also heard that the line guys will short a line to ground while working on it -- even if it's supposedly disconnected. I've also heard that if a home owner is found to be back feeding to the grid, they will disconnect the person from the grid, and it takes many months to get the guy hooked back up.

[JohnR66]

Yep. Lineman have been killed due to backfeeding from generaters. Use a transfer switch!

Here are some videos of power distribution tests and accidents. Check out the quarter shrinker too! http://205.243.100.155/frames/longarc.htmJohn